Basschat 112 Mk3 Questions

[chyc]

A week or so ago I asked some questions about building a BFM Jack 112 and got some very helpful answers from the community. The main question was "can I put a Faital 12PR320 into it?" To which the general answer was "yes, but....."

 

As a happy coincidence, there is a cabinet that does take the Faital 12PR320, the Basschat 112 Mk3! I'm now torn between which one to build. As sound is so subjective I'll put that to one side, assuming I'll like the sound of both. It's the build process that interests me. I have a table saw, a circular saw and a jigsaw, a soldering iron, and absolutely no experience with any of them! They are all borrowed for the purposes of this project.

 

1. Crossover: The BC112 crossover is a significant portion of the build process. I would say that BFM's crossover is within my capability, but the snake-pit of cables and pool of solder I would normally leave makes the BC112 beyond me. Is there anyone on this channel who would be prepared to make a BC112mk3 crossover for me and if so how much would it cost? I've roughly costed up both builds and the BC112 is cheaper, but it's close and this may tip the scales the other way given the difference between buying parts and buying a prebuilt BFM crossover at speakerhardware.com

 

2. Ply: 15mm looks to be elusive in all the places I'm looking. Am I just not looking hard enough? I'm not the kind of player to shred speakers: I've survived on the AI 1x10 so far, so with that in mind, would I get away with 12mm? Assuming this is OK, I can account for the change in size due to the box dimensions changing, but will I need to change the bracing design (or said another way are the dimensions sensitive enough to be affected by the change in width of the bracing?)

 

3. Back plate: I cannot visualize what's going on here. There's no mention of what connector to buy in the Part list. Is it just one Speakon that's drilled into the scrap ply left over from the horn cutout?

 

4. Wire: Mostly moot if I can get the crossover pre-built, but what wire do I use to wire this all up internally? I'm fairly new to all this and I intend on going to Wilko's to buy their "speaker cable" and split the two wires, irrespective of which design I end up building.

 

5. CNC and glue: I obviously don't want to start if the tolerances are such that a CNC build is required. The instructions say to use wood glue, and NOT to use PU. By contrast BFM says to use PU and NOT to use wood glue. I can understand the reasoning for both, but given that I won't be CNCing and the PU is designed to fill the gaps in the imperfections in the cut, would I get away with cutting using saws and using PU? I already have a bottle of both glues.

 

 

 

 

 

 

[Phil Starr]

There's one other difference between the cabs that you don't mention. Bill's is a commercial design and so you get detailed instructions and a level of support you don't get from our 'amateur designs. We can help you out on details if you get stuck but there isn't anyone full time able to do everything.

 

15mm was specified as the right balance between weight saving and rigidity. 18mm and 12mm are what the big sheds provide as standard. 12mm is lighter but you might get some panel resonances and need a bit more bracing. 18mm a little stiffer and you could possibly use a different bracing but we haven't tried and tested anything other than 15mm. It's not a huge risk building in either; both will work in the sense of giving you a decent sounding cab  but you might need to do some fettling after you have tested it to get the absolute best out of the ply that you try. Stevie specified poplar ply for his cabs and bought high grade ply for the final iteration. Good quality 12mm hardwood ply might not be too far short in terms of performance, we just haven't tested it.

 

The advantage of a self build is that you can choose the back panel of your choice, with an 8ohm speaker I'd always use a double socket so that I could daisy chain a second speaker but that is a choice for you. Our problem is that if we specify every component then designs become outdated as soon as one of those becomes unavailable.

 

You can get carried away with wire. Almost anything you use will have better current carrying ability than the very fine wires used in the speaker coil and they aren't long enough to have a huge resistance. I've more or less settled on standard 42 strand copper cable but it's not unknown for me to strip out the conductors from 13A mains cable and use those if I've nothing else to hand.

 

As to glue again don't get too hung up about it, almost any glue will be stronger than the wood. PU glue is horrible to work with and if you have gaps to fill you can always go back to them with mastic and seal them. If you use PU to bridge gaps then it loses strength. This isn't really about the right or wrong of a particular adhesive just about practical solutions.

 

If you possibly can ring around and try and find someone to cut the six pieces that make up the cab plus the two large pieces that make the main braces. I've built many cabs using the tools you have but unless your table saw has a sliding table it's unlikely you will cut 100% accurately on your first attempt. Even that isn't the end of the world as you can fix most thigs with a lot of sanding and maybe an extra trim but that bit isn't a lot of fun, working with accurately square cut panels is fun

[chyc]

Thank you Phil for your helpful answers. As I read up on its build process, the BC112mk3 and its instructions are complete in the sense that there's no ambiguity and two different but skilled woodworkers would end up with identical performing boxes finished to the same standard. I definitely do not class myself in that category.

 

At the same time you are absolutely correct that BFM plans include step by step instructions compared with a parts list, dimensions and cutting list for the BC112mk3. As I've already paid for the BFM plans I cannot factor the plans' cost into the build cost comparison, although conversely I will resist temptation to fall into the sunk cost fallacy trap.

 

For the benefit of those reading, there are some things that are huge (IMHO) benefits of choosing the BC design:

 

1. Metric units: Yes, I can convert from one measurement to another, but it almost seems like willful obstinence that the BFM designs only have imperial units. The BFM forums say that there are online converters, which is fine, but given that these are commercial plans and so you are not allowed to share it, this means that everyone who wants to convert has to do this individually and cannot give back to the community, even if they wanted to.
2. Angular cuts: BC112 seems to be straight cuts (with two very notable exceptions). The Jack baffle is rather daunting (this is one sheet of ply) and I would say getting this precise is more important than the BC112 bracing, which is a similar concept of a window frame design. Also the BFM has straight cuts with the edge at an angle. One is 23°, and there are optional cuts at 66° and 24°. The plans say you can complete the build without a table saw, but I would say this needs to be caveated with the fact that your circular saw needs to do arbitrary angles to the horizontal, which my one cannot.
3. Vertical dispersion: Much is made of Jack's meld array with its 120° horizontal dispersion.  The BC112 uses a horn with a smaller 90° horizontal dispersion. However, a meld array smooths out its high response by putting loads of piezos in a vertial stack, which compromises horizontal (Update: vertical) dispersion. There is no data on BFM's plans as to vertical dispersion but the top and bottom piezos will be 10" apart, so it's probably going to be a laser beam! This won't be so good for a bass cabinet on the floor with an amp on top. The BC112's PH-170 has 65° vertical dispersion. To be fair to the Jack, there's no free lunch and the plans say as much; there's an option to dial back the number of piezos to increase vertical dispersion at the expense of high frequency sensitivity.

In conclusion, there is no conclusion. I wake up each day thinking something different. Probably in the end the Jack 112 will win out basically because of the crossover, but I hope that my ramblings will help people after me reach an independent decision, crucially before sinking any money into the BFM plans like I did.

 

 

 

 

Edited August 29, 2022 by chyc
See "Update:"

[chyc]

Let me add a 4. Parts availability: The Jack 112 is built around an American supply-chain, compared with the BC112mk3 which was designed for building in the UK. For the Jack, the woofers are Eminence and the piezos are much, much cheaper in the US than here in these fair shores, and you need to buy loads for the meld array. Whether the Faital Pro 12PR320 can go toe to toe with the Eminence Kappalite 3012 is not really a fair question as they're not the same and probably have different goals, and the BFM gives a range of options so there's something for every price point but I cannot shake the feeling that adjusting parts for the same cost (to me in the UK), I'd end up with nicer components for the BC112 than the Jack.

[Marty Forrer]

I built my 600 watt 2x12 cab with 12mm ply and have had no resonance problems at all. I braced all the large panels, glued and screwed using PVA, and it weighs 18kg with the neo speakers. Using 15mm ply would have added a few kg, and using 18mm was out of the question for an old fart like me, and certainly not necessary.

[chyc]

4 hours ago, Marty Forrer said:

I built my 600 watt 2x12 cab with 12mm ply and have had no resonance problems at all. I braced all the large panels, glued and screwed using PVA, and it weighs 18kg with the neo speakers. Using 15mm ply would have added a few kg, and using 18mm was out of the question for an old fart like me, and certainly not necessary.

Thanks for that. I assume this is a different design and not a cut-n-shut on 2 x BC112mk3.

 

18kg is impressive for a 2x12!

[bertbass]

I built a pair of Jack lite 12s and these are made from 1/4" (6mm) ply.  With the Eminence drivers and horns they weigh in at 28 pounds each.  All the drivers I bought from Blue Aran here in the UK as well as all the crossover components.  I've used them for PA and they've been brilliant.  without the horns they would be a one finger lift and I probably wouldn't need the horns for bass use.  An easy built as well.

[stevie]

Some of this duplicates what Phil has said, but here goes...

 

1. Crossover

For anyone who has assembled an electronic kit, etc. in the past, the crossover is fairly straightforward to build, although doing point-to-point wiring is time-consuming. I do appreciate it's a step too far for most people, which is why I offered ready-built crossovers as part of the kit. Building one-off hardwired crossovers is out of the question now (it's half a day's work), but I've recently acquired a PCB facility, which means I could assemble one on a PCB without too much problem at a reasonable cost.

 

2. Ply

15mm poplar was chosen as a reasonable compromise between weight and stiffness, but there's nothing to stop you using 12mm or 18m. 12mm will be more resonant but lighter; 18mm will be less resonant but heavier. I'm happy that 15mm poplar was the right choice for that size of cab. The quality of the plywood is probably more important than the thickness. Go for the best quality you can get. The plywood offered by most local timber merchants is normally not good enough. If you can't get 15mm, you're probably shopping in the wrong place.

 

3. Back plate

The input connectors are Speakons. In the first prototype I built, I mounted a Speakon on a small piece of plywood, cut a hole in the back panel, and then glued the piece of plywood with the Speakon behind it. Then I rounded off the hole for cosmetic purposes. It worked fine and looked neat.

I wonder if you're referring to the input panel arrangement in the kit. That was CNC'd and would be difficult to replicate any other way. You could just fit one of the standard backplates available from the usual suppliers.

 

4. Wire

I suggest you use 1.5mm colour-coded twin core speaker cable. Avoid the copper coated aluminium stuff.

 

5. CNC and glue

PU glue is great if you want something that sets quickly. I have a tube in my workshop and wouldn't be without it. I suspect Bill recommends it because it expands and helps fill the gaps in the angled joints. But it is messy stuff. It sometimes sets too fast for comfort and oozes out all over the place. I think you'll find PVA easier to use.

 

 

 

[Chienmortbb]

Just to add a comment about wire, I buy two core mains cable 1.5mm for Ann my speaker needs. Mains cable from a reputable electrical supplier will be copper (don’t worry about the oxygen free baloney, all

copper cable has a little oxygen in it).  For some reason it seems only some commercial speaker cable is CCA. 
 

1.5mm mains cable is rated at about 18 amps, so good for 2500 watts into 8 ohms or 1250 watts into 4 ohms and the resistance of around a metre will

be negligible. 

Edited September 2, 2022 by Chienmortbb